Vibrating fork point level switches are in widespread use as a means for detecting when an interface between media in a process vessel is at a particular level within the vessel. The interface may, for example, be between a liquid and a gas, typically air, present above the liquid surface. When the interface between the liquid and the gas reaches the position of the switch, the operating frequency of the switch is affected. The change of frequency is sensed and a switching and/or alarm signal generated.
At present vibrating fork point level switches are configured to operate between a single ‘wet’ condition and a single ‘dry’ condition however in many applications in which vibrating point level switches are used, a variety of interfaces may be present. For example, in oil separators, oil is separated from water and sludge displaced during the extraction of the oil. There is thus one interface between the sludge and the water and another between the water and the oil. An operator may also wish to differentiate when a sensor is in contact with air as well as when the sensor is in contact with either oil, water or sludge.
It is an object of this invention to provide a level switch that will go at least some way to addressing the aforementioned wish; or which will at least provide a novel and useful choice.